JPH0142912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention involves mixing ceramic powder with an organic binder composed of a mixture of various waxes and polymers, imparting fluidity to the mixture, and injection molding the mixture. The present invention relates to a method for degreasing a ceramic green molded body, which removes an organic binder from a ceramic green molded body obtained by injection molding using a machine.

BACKGROUND ART In recent years, when molding ceramics, injection molding methods have been used to produce products with complex shapes and in large quantities.

In this method, ceramic powder and an organic binder are mixed to give fluidity to the mixture, which is then injection molded to obtain a green molded body. The organic binder must be removed from this before entering.

Problems to be Solved by the Invention However, this degreasing process is not easy and is the process in which defects such as blistering (foaming) and cracks are most likely to occur in the green molded product.

To avoid this defect, in this degreasing process,
Conventionally, with a slow heating rate of 1℃/h to 10℃/h,
The temperature of the degreasing furnace is adjusted to thermally decompose the organic binder and volatilize it to prevent defects.

However, this is the most time-consuming step in the injection molding process and is not efficient.

Usually, organic binders are used in combination with various waxes and polymers, but each has its own unique boiling point or thermal decomposition temperature, so the weight reduction can be uniformly achieved using the organic binder. This is a temperature range in which weight loss occurs rapidly due to the organic binder, and defects such as blistering (foaming) and cracking are particularly likely to occur in this temperature range.

As a countermeasure for this, a temperature increase program is set, such as degreasing by raising the temperature in a certain temperature range at a significantly slower rate than in other temperature ranges, depending on the thermal decomposition characteristics of the organic binder. Alternatively, organic binders with different weight loss temperature ranges are skillfully combined to select organic binders so that a constant change in weight loss can be obtained as a whole.

However, with this measure, the former has the disadvantage that the degreasing time becomes longer as a result of including a temperature raising step that is unnecessarily slower than the normal temperature raising rate.

The latter method has the disadvantage that combinations of organic binders are very difficult and limited, such as not being able to obtain good green molded products because the degreasing properties and flow properties of the organic binders are not balanced.

Means for Solving the Problems The present invention was developed under these circumstances, and it is possible to measure the weight change of a green molded product while degreasing an organic binder, and at the same time, The temperature increase rate is adjusted by feeding back this to the temperature increase rate of the degreasing furnace so that the time change in weight loss, that is, the differential weight change value per unit time of the green molded body, is within a constant range. Therefore, the purpose is to prevent as much as possible a sudden change in weight during degreasing, to prevent blistering (foaming) and cracks in the green molded product, and to efficiently control the degreasing time.

Embodiment The structure and operation thereof will be described in more detail based on the drawings.

The green molded product obtained by the injection molding machine is first placed in a degreasing furnace equipped with a load cell that measures weight loss.

By adjusting the heater of the degreasing furnace, temperature increase is started at a preset temperature increase rate, for example, 20° C./h.

Normally, if the temperature of the degreasing furnace is raised at a constant temperature increase rate of 20°C/h, the differential weight change value B of the green molded body per unit time, that is, B weight/ The time does not change and is constant at the beginning, but it varies greatly from point a to point c. This is the maximum value at point b.

Therefore, the temperature increase rate is adjusted by feeding back this value to the temperature increase rate A so that the differential weight change value B of the green molded body becomes approximately constant as shown in FIG.

That is, in Fig. 2, the temperature increase rate A is initially set at a fast rate of 20°C/h or more up to point a', but is gradually set at a slower rate from point a' to point b'. , Further, from point b' to point c', the speed is set to be slower than the initial speed, but gradually faster than the speed from point a' to point b'.

In this way, the thermal decomposition and volatilization of the organic binder from the green molded body can be carried out at a constant rate, thereby preventing defects such as blistering (foaming) and cracking due to variations in the desorption of the organic binder. It is also possible to improve the efficiency of degreasing time.

The present invention may be carried out in air or in an atmosphere of nitrogen gas, or under normal pressure, pressurization, or vacuum conditions, depending on the case. .

The effects of the present invention will be explained.

The present invention does not have the drawback that it takes a long time to degrease the organic binder of the ceramic green molded product, and it can be done efficiently at a constant speed. Ceramic products with complex shapes and large wall thickness changes can be obtained efficiently and in high yield without causing any problems.

Further, according to the present invention, the selection range of organic binders is widened, and it becomes possible to obtain ceramic products with good dimensional and shape changes that could not be formed using conventional organic binders.

[Brief explanation of drawings]

FIG. 1 is a graph regarding time and temperature when degreasing is carried out at a constant temperature increase rate, and FIG. 2 is a graph when the differential weight change value is kept constant. A... Temperature of the degreasing furnace, B... Differential weight change value per unit time, C... Weight.

Claims (1)

[Claims] 1. From a green molded body obtained by molding a mixture of ceramic powder and an organic binder made of a mixture of various waxes and polymers, the change in weight of the green molded body was measured when the organic binder was degreased. While degreasing the ceramic green molded body, this is fed back to the heating rate of the degreasing furnace to adjust the heating rate so that the differential weight change value per unit time of the green molded body is approximately constant. Method.